Talk:Cell Division - Meiosis
10 Most Recent Papers
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Distinct prophase arrest mechanisms in human male meiosis
Jan SZ1, Jongejan A2, Korver CM1, van Daalen SKM1, van Pelt AMM1, Repping S1, Hamer G3. Author information Abstract To prevent chromosomal aberrations being transmitted to the offspring, strict meiotic checkpoints are in place to remove aberrant spermatocytes. However, in about 1% of males these checkpoints cause complete meiotic arrest leading to azoospermia and subsequent infertility. Here, we unravel two clearly distinct meiotic arrest mechanisms that occur during prophase of human male meiosis. Type I arrested spermatocytes display severe asynapsis of the homologous chromosomes, disturbed XY-body formation and increased expression of the Y chromosome-encoded gene ZFY and seem to activate a DNA damage pathway leading to induction of p63, possibly causing spermatocyte apoptosis. Type II arrested spermatocytes display normal chromosome synapsis, normal XY-body morphology and meiotic crossover formation but have a lowered expression of several cell cycle regulating genes and fail to silence the X chromosome-encoded gene ZFX Discovery and understanding of these meiotic arrest mechanisms increases our knowledge of how genomic stability is guarded during human germ cell development. KEYWORDS: Human spermatogenesis; Infertility; Meiosis; Meiotic arrest; Meiotic silencing; p63
Actin cytoskeleton dynamics in mammalian oocyte meiosis
Biol Reprod. 2018 Jul 13. doi: 10.1093/biolre/ioy163. [Epub ahead of print]
Duan X1, Sun SC1.
During mitosis, cells undergo symmetrical cell division, while oocyte meiotic maturation undergoes two consecutive, asymmetric divisions that generate a totipotent haploid oocyte and two small polar bodies not involved in DNA replication. This specialized division allows most maternal components be maintained in the oocytes for early embryo development. Nuclear positioning, germinal vesicle breakdown, spindle migration, spindle rotation, chromosome segregation, and polar body extrusion are the most critical cellular processes during oocyte meiosis I and II, and a growing number of studies primarily using the mouse oocyte model revealed that actin filaments were critical for these processes, especially for spindle migration. Several important molecules have been reported to be involved in these processes. One family of molecules are the small GTPases, such as Rho GTPases, Ran GTPases, and Rab GTPases and another are the actin nucleators, such as the formin family and the Arp2/3 complex. The present review summarizes recent progress made regarding the roles of actin filaments in the asymmetric oocyte division. PMID: 30010726 DOI: 10.1093/biolre/ioy163
Calcium Signaling During Meiotic Cell Cycle Regulation and Apoptosis in Mammalian Oocytes
J Cell Physiol. 2017 May;232(5):976-981. doi: 10.1002/jcp.25670. Epub 2016 Nov 20.
Tiwari M1, Prasad S1, Shrivastav TG2, Chaube SK1.
Calcium (Ca++ ) is one of the major signal molecules that regulate various aspects of cell functions including cell cycle progression, arrest, and apoptosis in wide variety of cells. This review summarizes current knowledge on the differential roles of Ca++ in meiotic cell cycle resumption, arrest, and apoptosis in mammalian oocytes. Release of Ca++ from internal stores and/or Ca++ influx from extracellular medium causes moderate increase of intracellular Ca++ ([Ca++ ]i) level and reactive oxygen species (ROS). Increase of Ca++ as well as ROS levels under physiological range trigger maturation promoting factor (MPF) destabilization, thereby meiotic resumption from diplotene as well as metaphase-II (M-II) arrest in oocytes. A sustained increase of [Ca++ ]i level beyond physiological range induces generation of ROS sufficient enough to cause oxidative stress (OS) in aging oocytes. The increased [Ca++ ]i triggers Fas ligand-mediated oocyte apoptosis. Further, OS triggers mitochondria-mediated oocyte apoptosis in several mammalian species. Thus, Ca++ exerts differential roles on oocyte physiology depending upon its intracellular concentration. A moderate increase of [Ca++ ]i as well as ROS mediate spontaneous resumption of meiosis from diplotene as well as M-II arrest, while their high levels cause meiotic cell cycle arrest and apoptosis by operating both mitochondria- as well as Fas ligand-mediated apoptotic pathways. Indeed, Ca++ regulates cellular physiology by modulating meiotic cell cycle and apoptosis in mammalian oocytes. J. Cell. Physiol. 232: 976-981, 2017. © 2016 Wiley Periodicals, Inc.
© 2016 Wiley Periodicals, Inc.
PMID 27791263 DOI: 10.1002/jcp.25670
Kif4 Is Essential for Mouse Oocyte Meiosis
PLoS One. 2017 Jan 26;12(1):e0170650. doi: 10.1371/journal.pone.0170650. eCollection 2017.
Camlin NJ1,2, McLaughlin EA1,2,3, Holt JE2,4.
Progression through the meiotic cell cycle must be strictly regulated in oocytes to generate viable embryos and offspring. During mitosis, the kinesin motor protein Kif4 is indispensable for chromosome condensation and separation, midzone formation and cytokinesis. Additionally, the bioactivity of Kif4 is dependent on phosphorylation via Aurora Kinase B and Cdk1, which regulate Kif4 function throughout mitosis. Here, we examine the role of Kif4 in mammalian oocyte meiosis. Kif4 localized in the cytoplasm throughout meiosis I and II, but was also observed to have a dynamic subcellular distribution, associating with both microtubules and kinetochores at different stages of development. Co-localization and proximity ligation assays revealed that the kinetochore proteins, CENP-C and Ndc80, are potential Kif4 interacting proteins. Functional analysis of Kif4 in oocytes via antisense knock-down demonstrated that this protein was not essential for meiosis I completion. However, Kif4 depleted oocytes displayed enlarged polar bodies and abnormal metaphase II spindles, indicating an essential role for this protein for correct asymmetric cell division in meiosis I. Further investigation of the phosphoregulation of meiotic Kif4 revealed that Aurora Kinase and Cdk activity is critical for Kif4 kinetochore localization and interaction with Ndc80 and CENP-C. Finally, Kif4 protein but not gene expression was found to be upregulated with age, suggesting a role for this protein in the decline of oocyte quality with age.
PMID 28125646 PMCID: PMC5268449 DOI: 10.1371/journal.pone.0170650
Higher Order Oligomerization of the Licensing ORC4 Protein Is Required for Polar Body Extrusion in Murine Meiosis
J Cell Biochem. 2017 Feb 23. doi: 10.1002/jcb.25949. [Epub ahead of print]
Nguyen H1, James NG2, Nguyen L1, Nguyen TP1, Vuong C1, Ortega M3, Ward WS1,4.
We have previously shown that the DNA replication licensing factor ORC4 forms a cage around the chromosomes that are extruded in both polar bodies during murine oogenesis, but not around the chromosomes that are retained in the oocyte or around the sperm chromatin. We termed this structure the ORC4 cage. Here, we tested whether the formation of the ORC4 cage is necessary for polar body extrusion (PBE). We first experimentally forced oocytes to extrude sperm chromatin as a pseudo-polar body and found that under these conditions the sperm chromatin did become enclosed in an ORC4 cage. Next, we attempted to prevent the formation of the ORC4 cage by injecting peptides that contained sequences of different domains of the ORC4 protein into metaphase II oocytes just before the cage normally forms. Our rationale was that the ORC4 peptides would block protein-protein interactions required for cage formation. Two out of six tested peptides prevented the ORC4 cage formation and simultaneously inhibited polar body extrusion (PBE), resulting in the formation of two pronuclei that were retained in the oocyte. Together, these data demonstrate that ORC4 oligomerization is required to form the ORC4 cage and that it is required for PBE. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
KEYWORDS: Meiosis; ORC4; oocyte; polar body extrusion PMID 28230328 DOI: 10.1002/jcb.25949
The evolution of meiotic sex and its alternatives
Proc Biol Sci. 2016 Sep 14;283(1838). pii: 20161221. doi: 10.1098/rspb.2016.1221.
Mirzaghaderi G1, Hörandl E2.
Meiosis is an ancestral, highly conserved process in eukaryotic life cycles, and for all eukaryotes the shared component of sexual reproduction. The benefits and functions of meiosis, however, are still under discussion, especially considering the costs of meiotic sex. To get a novel view on this old problem, we filter out the most conserved elements of meiosis itself by reviewing the various modifications and alterations of modes of reproduction. Our rationale is that the indispensable steps of meiosis for viability of offspring would be maintained by strong selection, while dispensable steps would be variable. We review evolutionary origin and processes in normal meiosis, restitutional meiosis, polyploidization and the alterations of meiosis in forms of uniparental reproduction (apomixis, apomictic parthenogenesis, automixis, selfing) with a focus on plants and animals. This overview suggests that homologue pairing, double-strand break formation and homologous recombinational repair at prophase I are the least dispensable elements, and they are more likely optimized for repair of oxidative DNA damage rather than for recombination. Segregation, ploidy reduction and also a biparental genome contribution can be skipped for many generations. The evidence supports the theory that the primary function of meiosis is DNA restoration rather than recombination. © 2016 The Authors. KEYWORDS: apomixis; automixis; paradox of sex; restitutional meiosis; selfing
PMID 27605505 PMCID: PMC5031655 DOI: 10.1098/rspb.2016.1221
From Meiosis to Mitosis: The Astonishing Flexibility of Cell Division Mechanisms in Early Mammalian Development
Curr Top Dev Biol. 2016;120:125-71. doi: 10.1016/bs.ctdb.2016.04.011. Epub 2016 Jun 22.
Bury L1, Coelho PA2, Glover DM2.
The execution of female meiosis and the establishment of the zygote is arguably the most critical stage of mammalian development. The egg can be arrested in the prophase of meiosis I for decades, and when it is activated, the spindle is assembled de novo. This spindle must function with the highest of fidelity and yet its assembly is unusually achieved in the absence of conventional centrosomes and with minimal influence of chromatin. Moreover, its dramatic asymmetric positioning is achieved through remarkable properties of the actin cytoskeleton to ensure elimination of the polar bodies. The second meiotic arrest marks a uniquely prolonged metaphase eventually interrupted by egg activation at fertilization to complete meiosis and mark a period of preparation of the male and female pronuclear genomes not only for their entry into the mitotic cleavage divisions but also for the imminent prospect of their zygotic expression. © 2016 Elsevier Inc. All rights reserved. KEYWORDS: Acentriolar MTOCs; Egg activation; Fertilization; Meiotic maturation; Meiotic reactivation; Meiotic spindle assembly; Meiotic spindle positioning; Metaphase II arrest; Prophase arrest; Spindle assembly checkpoint
Silencing of X-Linked MicroRNAs by Meiotic Sex Chromosome Inactivation
PLoS Genet. 2015 Oct 28;11(10):e1005461. doi: 10.1371/journal.pgen.1005461. eCollection 2015.
Royo H1, Seitz H2, ElInati E3, Peters AH4, Stadler MB5, Turner JM3.
During the pachytene stage of meiosis in male mammals, the X and Y chromosomes are transcriptionally silenced by Meiotic Sex Chromosome Inactivation (MSCI). MSCI is conserved in therian mammals and is essential for normal male fertility. Transcriptomics approaches have demonstrated that in mice, most or all protein-coding genes on the X chromosome are subject to MSCI. However, it is unclear whether X-linked non-coding RNAs behave in a similar manner. The X chromosome is enriched in microRNA (miRNA) genes, with many exhibiting testis-biased expression. Importantly, high expression levels of X-linked miRNAs (X-miRNAs) have been reported in pachytene spermatocytes, indicating that these genes may escape MSCI, and perhaps play a role in the XY-silencing process. Here we use RNA FISH to examine X-miRNA expression in the male germ line. We find that, like protein-coding X-genes, X-miRNAs are expressed prior to prophase I and are thereafter silenced during pachynema. X-miRNA silencing does not occur in mouse models with defective MSCI. Furthermore, X-miRNAs are expressed at pachynema when present as autosomally integrated transgenes. Thus, we conclude that silencing of X-miRNAs during pachynema in wild type males is MSCI-dependent. Importantly, misexpression of X-miRNAs during pachynema causes spermatogenic defects. We propose that MSCI represents a chromosomal mechanism by which X-miRNAs, and other potential X-encoded repressors, can be silenced, thereby regulating genes with critical late spermatogenic functions.
Meiotic Recombination: The Essence of Heredity
Cold Spring Harb Perspect Biol. 2015 Oct 28. pii: a016618. doi: 10.1101/cshperspect.a016618. [Epub ahead of print]
The study of homologous recombination has its historical roots in meiosis. In this context, recombination occurs as a programmed event that culminates in the formation of crossovers, which are essential for accurate chromosome segregation and create new combinations of parental alleles. Thus, meiotic recombination underlies both the independent assortment of parental chromosomes and genetic linkage. This review highlights the features of meiotic recombination that distinguish it from recombinational repair in somatic cells, and how the molecular processes of meiotic recombination are embedded and interdependent with the chromosome structures that characterize meiotic prophase. A more in-depth review presents our understanding of how crossover and noncrossover pathways of meiotic recombination are differentiated and regulated. The final section of this review summarizes the studies that have defined defective recombination as a leading cause of pregnancy loss and congenital disease in humans. Copyright © 2015 Cold Spring Harbor Laboratory Press; all rights reserved.
Nat Commun. 2015 Jul 1;6:7550. doi: 10.1038/ncomms8550.
Sakakibara Y1, Hashimoto S2, Nakaoka Y2, Kouznetsova A3, Höög C3, Kitajima TS1.
The frequency of chromosome segregation errors during meiosis I (MI) in oocytes increases with age. The two-hit model suggests that errors are caused by the combination of a first hit that creates susceptible crossover configurations and a second hit comprising an age-related reduction in chromosome cohesion. This model predicts an age-related increase in univalents, but direct evidence of this phenomenon as a major cause of segregation errors has been lacking. Here, we provide the first live analysis of single chromosomes undergoing segregation errors during MI in the oocytes of naturally aged mice. Chromosome tracking reveals that 80% of the errors are preceded by bivalent separation into univalents. The set of the univalents is biased towards balanced and unbalanced predivision of sister chromatids during MI. Moreover, we find univalents predisposed to predivision in human oocytes. This study defines premature bivalent separation into univalents as the primary defect responsible for age-related aneuploidy.
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Premature dyad separation in meiosis II is the major segregation error with maternal age in mouse oocytes
Development. 2014 Jan;141(1):199-208. doi: 10.1242/dev.100206.
Yun Y1, Lane SI, Jones KT.
As women get older their oocytes become susceptible to chromosome mis-segregation. This generates aneuploid embryos, leading to increased infertility and birth defects. Here we examined the provenance of aneuploidy by tracking chromosomes and their kinetochores in oocytes from young and aged mice. Changes consistent with chromosome cohesion deterioration were found with age, including increased interkinetochore distance and loss of the centromeric protector of cohesion SGO2 in metaphase II arrested (metII) eggs, as well as a rise in the number of weakly attached bivalents in meiosis I (MI) and lagging chromosomes at anaphase I. However, there were no MI errors in congression or biorientation. Instead, premature separation of dyads in meiosis II was the major segregation defect in aged eggs and these were associated with very low levels of SGO2. These data show that although considerable cohesion loss occurs during MI, its consequences are observed during meiosis II, when centromeric cohesion is needed to maintain dyad integrity. KEYWORDS: Chromosomes; Imaging; Meiosis; Mouse; Oocyte
© 2014. Published by The Company of Biologists Ltd This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
WASH complex regulates Arp2/3 complex for actin-based polar body extrusion in mouse oocytes
Sci Rep. 2014 Jul 7;4:5596. doi: 10.1038/srep05596.
Wang F1, Zhang L1, Zhang GL2, Wang ZB2, Cui XS3, Kim NH3, Sun SC1.
Prior to their fertilization, oocytes undergo asymmetric division, which is regulated by actin filaments. Recently, WASH complex were identified as actin nucleation promoting factors (NPF) that activated Arp2/3 complex. However, the roles of WASH complex remain uncertain, particularly for oocyte polarization and asymmetric division. Here, we examined the functions of two important subunits of a WASH complex, WASH1 and Strumpellin, during mouse oocyte meiosis. Depleting WASH1 or disrupting Strumpellin activity by WASH1 morpholino (MO) injection or Strumpellin antibody injection decreased polar body extrusion and caused oocyte symmetric division, and this may have been due to spindle formation and migration defects. Time lapse microscopy showed that actin filaments distribution and relative amount at the membrane and in the cytoplasm of oocytes was significantly decreased after disrupting WASH complex. In addition, Arp2/3 complex expression was reduced after WASH1 depletion. Thus, our data indicated that WASH complex regulated Arp2/3 complex and were required for cytokinesis and following polar body extrusion during mouse oocyte meiotic maturation. PMID 24998208
Retinoic acid regulation of male meiosis
Curr Opin Endocrinol Diabetes Obes. 2013 Jun;20(3):217-23. doi: 10.1097/MED.0b013e32836067cf.
Hogarth CA1, Griswold MD.
PURPOSE OF REVIEW: Description of new evidence to support the model for how retinoic acid regulates spermatogonial differentiation, male meiosis and the cycle of the seminiferous epithelium.
RECENT FINDINGS: It has been known since the 1920s that vitamin A is essential for spermatogenesis. However, only recently has significant progress been made toward understanding how the active metabolite of vitamin A, retinoic acid, regulates spermatogenesis at multiple different differentiation steps, including the onset of meiosis. Current publications suggest that the initiation and maintenance of the cycle of the seminiferous epithelium is linked to retinoic-acid-driving spermatogonial differentiation and meiotic onset.
SUMMARY: Retinoic acid appears to act in a pulsatile manner, periodically driving spermatogonial differentiation and meiotic onset at discrete points along testis tubules, and as a result, is likely to be responsible for generating and maintaining the cycle of the seminiferous epithelium.
Chromosomes in the Porcine First Polar Body Possess Competence of Second Meiotic Division within Enucleated MII Stage Oocytes
PLoS One. 2013 Dec 3;8(12):e82766. doi: 10.1371/journal.pone.0082766.
Lin T, Diao YF, Kang JW, Lee JE, Kim DK, Jin DI. Source Department of Animal Science & Biotechnology, Chungnam National University, Daejeon, Republic of Korea.
To determine whether chromosomes in the porcine first polar body (PB1) can complete the second meiotic division and subsequently undergo normal pre-implantation embryonic development, we examined the developmental competence of PB1 chromosomes injected into enucleated MII stage oocytes by nuclear transfer method (chromosome replacement group, CR group). After parthenogenetic activation (PA) or in vitro fertilization (IVF), the cleavage rate of reconstructed oocytes in the IVF group (CR-IVF group, 36.4 ± 3.2%) and PA group (CR-PA group, 50.8 ± 4.2%) were significantly lower than that of control groups in which normal MII oocytes were subjected to IVF (MII-IVF group, 75.8 ± 1.5%) and PA (MII-PA group, 86.9 ± 3.7%). Unfertilized rates was significantly higher in the CR-IVF group (48.6 ± 3.3%) than in the MII-IVF group (13.1 ± 3.4%). The blastocyst formation rate was 8.3 ± 1.9% in the CR-PA group, whereas no blastocyst formation was observed in the CR-IVF group. To produce tetraploid parthenogenetic embryos, intact MII stage oocytes injected with PB1chromosomes were electrically stimulated, treated with 7.5 μg/mL cytochalasin B for 3 h (MII oocyte + PB1 + CB group), and then cultured without cytochalasin B. The average cleavage rate of reconstructed oocytes was 72.5% (48 of 66), and the blastocyst formation rate was 18.7% (9 of 48). Chromosome analysis showed similar proportions of haploid and diploid cells in the control (normal MII oocytes) and CR groups after PA; overall, 23.6% of blastocysts were tetraploid in the MII oocyte + PB1 + CB group. These results demonstrate that chromosomes in PB1 can participate in normal pre-implantation embryonic development when injected into enucleated MII stage oocytes, and that tetraploid PA blastocysts are produced (although at a low proportion) when PB1 chromosomes are injected into intact MII stage oocytes.
Bora regulates meiotic spindle assembly and cell cycle during mouse oocyte meiosis
Mol Reprod Dev. 2013 Apr 23. doi: 10.1002/mrd.22185. [Epub ahead of print]
Zhai R, Yuan YF, Zhao Y, Liu XM, Zhen YH, Yang FF, Wang L, Huang CZ, Cao J, Huo LJ. Source Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction, Education Ministry of China, College of Animal Science and Technology, Huazhong Agricultural University, Wuhan, 430070, People's Republic of, China. Abstract Bora is the binding partner of Aurora A, which is required for its activation and phosphorylation of Polo like kinase 1 (Plk1), and is involved in the spindle assembly and progress of the cell cycle during mitosis. In this study, we examined the expression, localization, and function of Bora during mouse oocyte meiosis. The expression level of Bora was increased during oocyte meiotic maturation, with an elevated level at metaphase. Immunofluorescence analysis showed that Bora was concentrated as a dot shortly after germinal vesicle breakdown (GVBD), associating first with the surrounding chromosomes and then with the spindle throughout the oocyte meiotic maturation. Further experiments confirmed that Bora co-localized with α-tubulin at prometaphase/metaphase, but dissociated from α-tubulin at anaphase/telophase. In metaphase-II-arrested oocytes, Bora was evenly distributed in the cytoplasm after treatment with a microtubule-depolymerizing agent, or recruited to the spindle after treatment with a microtubule-polymerizing agent, indicating that Bora was physically connected to the meiotic spindle and α-tubulin at metaphase. Furthermore, inhibition or depletion of Bora by either anti-Bora antibody or siRNA microinjection significantly reduced the rates of GVBD and inhibited first polar body extrusion; caused morphologically defective spindles and misaligned chromosomes; arrested maturing oocytes at prometaphase/metaphase-I stage, or left oocytes and their first polar bodies with severely misaligned chromosomes and defective spindles; and/or caused the disappearance of Aurora A and Plk1 at the spindle. These results indicated that Bora acts as a critical regulator of Aurora A and Plk1, and is involved in microtubule organization during oocyte meiosis. Mol. Reprod. Dev. © 2013 Wiley Periodicals, Inc. Copyright © 2013 Wiley Periodicals, Inc.
Live births from isolated primary/early secondary follicles following a multi-step culture without organ culture in mice
Reproduction. 2013 Apr 23. [Epub ahead of print]
Mochida N, Hasegawa A, Saka K, Ogino M, Hosoda Y, Wada R, Sawai H, Shibahara H. Source N Mochida, Department of Obstetrics and Gynecology, Hyogo College of Medicine, Nishinomiya, Japan.
Although the ovary has a large store of germ cells, most of them do not reach mature stages. If a culture system could be developed from early growing follicles to mature oocytes, it would be useful for biological research as well as for reproductive medicine. This study was conducted to establish a multi-step culture system from isolated early growing follicles to mature oocytes using a mouse model. Early growing follicles with diameters of 60-95 μm corresponding to primary and early secondary follicles were isolated from 6-day-old mice and classified into three groups by diameter. These follicles contained oocytes with diameters of ~45 μm and one or a few layered granulosa cells on the basal lamina. Embedding in collagen gel was followed by first step culture. After 9-day culture, the growing follicles were transferred to the second step on collagen coated membrane. At day 17 of the culture series, the oocyte-granulosa cell complexes were subjected to in vitro maturation. Around 90 % of the oocytes in follicles surviving at day 17 resumed second meiosis (metaphase II oocytes : 49.0-58.7 %) regardless of the size when the follicle culture started. To assess developmental competence to live birth, the eggs were used for in vitro fertilization and implantation to pseudopregnant mice. We successfully obtained two live offspring that produced next generations after puberty. We thus conclude that the culture system reported here was able to induce growth of small follicles and the resultant mature oocytes were able to develop into normal mice.
Sequential actin-based pushing forces drive meiosis I chromosome migration and symmetry breaking in oocytes
J Cell Biol. 2013 Mar 4;200(5):567-76. doi: 10.1083/jcb.201211068. Epub 2013 Feb 25.
Yi K1, Rubinstein B, Unruh JR, Guo F, Slaughter BD, Li R.
Polar body extrusion during oocyte maturation is critically dependent on asymmetric positioning of the meiotic spindle, which is established through migration of the meiosis I (MI) spindle/chromosomes from the oocyte interior to a subcortical location. In this study, we show that MI chromosome migration is biphasic and driven by consecutive actin-based pushing forces regulated by two actin nucleators, Fmn2, a formin family protein, and the Arp2/3 complex. Fmn2 was recruited to endoplasmic reticulum structures surrounding the MI spindle, where it nucleated actin filaments to initiate an initially slow and poorly directed motion of the spindle away from the cell center. A fast and highly directed second migration phase was driven by actin-mediated cytoplasmic streaming and occurred as the chromosomes reach a sufficient proximity to the cortex to activate the Arp2/3 complex. We propose that decisive symmetry breaking in mouse oocytes results from Fmn2-mediated perturbation of spindle position and the positive feedback loop between chromosome signal-induced Arp2/3 activation and Arp2/3-orchestrated cytoplasmic streaming that transports the chromosomes.
Three-dimensional quantitative analysis of chromosomes in the oocytes of aging mice during meiosis I in vitro
Theriogenology. 2012 Nov 19. pii: S0093-691X(12)00467-0. doi: 10.1016/j.theriogenology.2012.08.010. [Epub ahead of print]
Tian N, Zhang L, Zheng JH, Lv DY, Li Y, Ma WY. Source Department of Physics, State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing, China.
The mechanism of senescence is very complicated and can involve formation of chromosome abnormalities and a decline in female fertility. In this study, 3-D visualization of fluorescently labeled chromosomes in oocytes from aging and pubertal mice during in vitro maturation was done with a two-photon laser scanning microscope. Differences between aging and pubertal groups at various maturation stages were analyzed quantitatively in terms of chromosomal morphology, shape, and spatial arrangement. Compared with the pubertal group, the chromosomal morphology of oocytes from aging mice changed: both the mean volume and the mean surface area of chromosomes increased by approximately 20% (P < 0.05) at prometaphase and metaphase of meiosis I (considered to be the weakly condensed folded form of the chromosomes). Furthermore, at these stages, the shape of the chromosomal array became rounder (roundness factor increased by approximately 10%; P < 0.001) and the adhesion among chromosomes became more severe (P < 0.001) at approximately the same stages. Additionally, trends over time for both chromosomal morphology and shape were quite distinct between oocytes from aging and pubertal mice. Interestingly, trends for mean distance were similar; therefore, aging did not seem to influence chromosome movement toward the metaphase plate. These morphologic results should be useful to study age-related degradation of oocyte quality and to interpret results derived from molecular biology. Copyright © 2012 Elsevier Inc. All rights reserved.
Meiosis errors in over 20,000 oocytes studied in the practice of preimplantation aneuploidy testing
Reprod Biomed Online. 2011 Jan;22(1):2-8. doi: 10.1016/j.rbmo.2010.08.014. Epub 2010 Sep 15.
Kuliev A1, Zlatopolsky Z, Kirillova I, Spivakova J, Cieslak Janzen J.
This study presents the world’s largest series of over 20,000 oocytes tested for aneuploidies, involving chromosomes 13,16, 18, 21 and 22, providing the data on the rates and types of aneuploidies and their origin. Almost every second oocyte (46.8%) is abnormal, with predominance of extra chromatid errors predicting predominance of trisomies (53%) over monosomies (26%) in the resulting embryos (2:1), which is opposite to monosomy predominance observed in embryo testing. Of the detected anomalies in oocytes, 40% are complex, so testing for a few most prevalent chromosome errors may allow detection of the majority of abnormal embryos. Chromosome 21 and 22 errors are more prevalent, while two different patterns of error origin were observed for different chromosomes: chromosome 16 and 22 errors originate predominantly from meiosis II, compared with chromosome 13, 18 and 21 errors originating from meiosis I. This provides the first evidence for the differences in the aneuploid embryo survival depending on the meiotic origin. Considering the problem of mosaicism, which is the major limitation of the cleavage-stage testing, the direct oocyte aneuploidy testing by polar body analysis may be of obvious practical value in improving accuracy and reliability of avoiding aneuploid embryos for transfer. Copyright © 2010 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.
Chiasmata promote monopolar attachment of sister chromatids and their co-segregation toward the proper pole during meiosis I
PLoS Genet. 2011 Mar;7(3):e1001329. doi: 10.1371/journal.pgen.1001329. Epub 2011 Mar 10.
Hirose Y, Suzuki R, Ohba T, Hinohara Y, Matsuhara H, Yoshida M, Itabashi Y, Murakami H, Yamamoto A. Source The Department of Chemistry, Shizuoka University, Shizuoka, Japan. Abstract The chiasma is a structure that forms between a pair of homologous chromosomes by crossover recombination and physically links the homologous chromosomes during meiosis. Chiasmata are essential for the attachment of the homologous chromosomes to opposite spindle poles (bipolar attachment) and their subsequent segregation to the opposite poles during meiosis I. However, the overall function of chiasmata during meiosis is not fully understood. Here, we show that chiasmata also play a crucial role in the attachment of sister chromatids to the same spindle pole and in their co-segregation during meiosis I in fission yeast. Analysis of cells lacking chiasmata and the cohesin protector Sgo1 showed that loss of chiasmata causes frequent bipolar attachment of sister chromatids during anaphase. Furthermore, high time-resolution analysis of centromere dynamics in various types of chiasmate and achiasmate cells, including those lacking the DNA replication checkpoint factor Mrc1 or the meiotic centromere protein Moa1, showed the following three outcomes: (i) during the pre-anaphase stage, the bipolar attachment of sister chromatids occurs irrespective of chiasma formation; (ii) the chiasma contributes to the elimination of the pre-anaphase bipolar attachment; and (iii) when the bipolar attachment remains during anaphase, the chiasmata generate a bias toward the proper pole during poleward chromosome pulling that results in appropriate chromosome segregation. Based on these results, we propose that chiasmata play a pivotal role in the selection of proper attachments and provide a backup mechanism that promotes correct chromosome segregation when improper attachments remain during anaphase I.
A review of trisomy X (47,XXX)
Tartaglia NR, Howell S, Sutherland A, Wilson R, Wilson L. Orphanet J Rare Dis. 2010 May 11;5:8. Review. PMID: 20459843 [ Trisomy X - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2883963/?tool=pubmed
A spindle assembly checkpoint protein functions in prophase I arrest and prometaphase progression
Science. 2009 Nov 13;326(5955):991-4.
Homer H, Gui L, Carroll J.
Oocyte and Embryo Research Laboratory, Department of Cell and Developmental Biology, Division of Biosciences and Institute for Women's Health, University College London, London, UK. email@example.com Abstract Two critical stages of mammalian oocyte regulation are prophase I arrest, which is important for sustaining the oocyte pool, and the progression through meiosis I (MI) to produce fertilizable eggs. We have found that the spindle assembly checkpoint protein BubR1 regulates both stages in mouse oocytes. We show that oocytes depleted of BubR1 cannot sustain prophase I arrest and readily undergo germinal vesicle breakdown, a marker for reentry into MI. BubR1-depleted oocytes then arrest before completing MI, marked by failure of polar body extrusion. Both meiotic defects in BubR1-depleted oocytes are due to reduced activity of the master regulator known as the anaphase-promoting complex (APC), brought about through diminished levels of the APC coactivator Cdh1.
Sperm chromatin-induced ectopic polar body extrusion in mouse eggs after ICSI and delayed egg activation
PLoS One. 2009 Sep 29;4(9):e7171.
Deng M, Li R.
Stowers Institute for Medical Research, Kansas City, Missouri, United States of America. Mdeng3@BICS.BWH.Harvard.edu Abstract Meiotic chromosomes in an oocyte are not only a maternal genome carrier but also provide a positional signal to induce cortical polarization and define asymmetric meiotic division of the oocyte, resulting in polar body extrusion and haploidization of the maternal genome. The meiotic chromosomes play dual function in determination of meiosis: 1) organizing a bipolar spindle formation and 2) inducing cortical polarization and assembly of a distinct cortical cytoskeleton structure in the overlying cortex for polar body extrusion. At fertilization, a sperm brings exogenous paternal chromatin into the egg, which induces ectopic cortical polarization at the sperm entry site and leads to a cone formation, known as fertilization cone. Here we show that the sperm chromatin-induced fertilization cone formation is an abortive polar body extrusion due to lack of spindle induction by the sperm chromatin during fertilization. If experimentally manipulating the fertilization process to allow sperm chromatin to induce both cortical polarization and spindle formation, the fertilization cone can be converted into polar body extrusion. This suggests that sperm chromatin is also able to induce polar body extrusion, like its maternal counterpart. The usually observed cone formation instead of ectopic polar body extrusion induced by sperm chromatin during fertilization is due to special sperm chromatin compaction which restrains it from rapid spindle induction and therefore provides a protective mechanism to prevent a possible paternal genome loss during ectopic polar body extrusion.
PMID: 19787051 http://www.ncbi.nlm.nih.gov/pubmed/19787051
A new model for asymmetric spindle positioning in mouse oocytes
Curr Biol. 2008 Dec 23;18(24):1986-92. doi: 10.1016/j.cub.2008.11.022. Epub 2008 Dec 8.
Schuh M1, Ellenberg J.
An oocyte matures into an egg by extruding half of the chromosomes in a small polar body. This extremely asymmetric division enables the oocyte to retain sufficient storage material for the development of the embryo after fertilization. To divide asymmetrically, mammalian oocytes relocate the spindle from their center to the cortex. In all mammalian species analyzed so far, including human, mouse, cow, pig, and hamster, spindle relocation depends on filamentous actin (F-actin). However, even though spindle relocation is essential for fertility, the involved F-actin structures and the mechanism by which they relocate the spindle are unknown. Here we show in live mouse oocytes that spindle relocation requires a continuously reorganizing cytoplasmic actin network nucleated by Formin-2 (Fmn2). We found that the spindle poles were enriched in activated myosin and pulled on this network. Inhibition of myosin activation by myosin light chain kinase (MLCK) stopped pulling and spindle relocation, indicating that myosin pulling creates the force that drives spindle movement. Based on these results, we propose the first mechanistic model for asymmetric spindle positioning in mammalian oocytes and validate five of its key predictions experimentally.
Meiotic regulation of TPX2 protein levels governs cell cycle progression in mouse oocytes
PLoS One. 2008 Oct 3;3(10):e3338.
Brunet S, Dumont J, Lee KW, Kinoshita K, Hikal P, Gruss OJ, Maro B, Verlhac MH.
UMR7622, Université Pierre et Marie Curie/CNRS, Bat. C, 5e, 9 quai Saint Bernard, Paris, France. Abstract Formation of female gametes requires acentriolar spindle assembly during meiosis. Mitotic spindles organize from centrosomes and via local activation of the RanGTPase on chromosomes. Vertebrate oocytes present a RanGTP gradient centred on chromatin at all stages of meiotic maturation. However, this gradient is dispensable for assembly of the first meiotic spindle. To understand this meiosis I peculiarity, we studied TPX2, a Ran target, in mouse oocytes. Strikingly, TPX2 activity is controlled at the protein level through its accumulation from meiosis I to II. By RNAi depletion and live imaging, we show that TPX2 is required for spindle assembly via two distinct functions. It controls microtubule assembly and spindle pole integrity via the phosphorylation of TACC3, a regulator of MTOCs activity. We show that meiotic spindle formation in vivo depends on the regulation of at least a target of Ran, TPX2, rather than on the regulation of the RanGTP gradient itself.
Impact of trisomy on fertility and meiosis in male mice
Hum Reprod. 2007 Feb;22(2):468-76. Epub 2006 Oct 17. Davisson M, Akeson E, Schmidt C, Harris B, Farley J, Handel MA.
The Jackson Laboratory, Bar Harbor, ME 04609, USA. firstname.lastname@example.org Abstract BACKGROUND: Chromosomal abnormalities frequently are associated with impairment or arrest of spermatogenesis in mammals but are compatible with fertility in female carriers of the same anomaly. In the case of trisomy, mice have extra genomic DNA as well as the chromosomal abnormality, usually present as an extra, unpaired chromosome. Thus, impairment of spermatogenesis in trisomic males could be due to the presence of extra genomic material (i.e. triplicated genes) or due to the chromosomal abnormality and presence of an unpaired chromosome in meiosis.
METHODS: In this study, fertility and chromosomal pairing configurations during meiotic prophase were analysed in male mice trisomic for different segments of the genome. Four have an extra segmental or tertiary trisomic chromosome--Ts(17(16))65Dn, Ts(10(16))232Dn, Ts(12(17))4Rk and Ts(4(17))2Lws--and one has the triplicated segment attached to another chromosome--Ts(16C-tel)1Cje. Ts(17(16))65Dn and Ts(16C-tel)1Cje have similar gene content triplication and differ primarily in whether the extra DNA is in an extra chromosome or not.
RESULTS: The presence of an intact extra chromosome, rather than trisomy per se, is associated with male sterility. Additionally, sterility is correlated with a high frequency of association of the unpaired chromosome with the XY body, which contains the largely unpaired X and Y chromosomes.
CONCLUSIONS: Intact extra chromosomes disrupt spermatogenesis, and unpaired chromosomes establish a unique chromatin territory within meiotic nuclei.
Mouse Emi2 is required to enter meiosis II by reestablishing cyclin B1 during interkinesis
J Cell Biol. 2006 Sep 11;174(6):791-801.
Madgwick S, Hansen DV, Levasseur M, Jackson PK, Jones KT.
Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle NE2 4HH, England, UK. email@example.com Abstract During interkinesis, a metaphase II (MetII) spindle is built immediately after the completion of meiosis I. Oocytes then remain MetII arrested until fertilization. In mouse, we find that early mitotic inhibitor 2 (Emi2), which is an anaphase-promoting complex inhibitor, is involved in both the establishment and the maintenance of MetII arrest. In MetII oocytes, Emi2 needs to be degraded for oocytes to exit meiosis, and such degradation, as visualized by fluorescent protein tagging, occurred tens of minutes ahead of cyclin B1. Emi2 antisense morpholino knockdown during oocyte maturation did not affect polar body (PB) extrusion. However, in interkinesis the central spindle microtubules from meiosis I persisted for a short time, and a MetII spindle failed to assemble. The chromatin in the oocyte quickly decondensed and a nucleus formed. All of these effects were caused by the essential role of Emi2 in stabilizing cyclin B1 after the first PB extrusion because in Emi2 knockdown oocytes a MetII spindle was recovered by Emi2 rescue or by expression of nondegradable cyclin B1 after meiosis I.
How eggs arrest at metaphase II: MPF stabilisation plus APC/C inhibition equals Cytostatic Factor http://www.celldiv.com/content/2/1/4
Mammalian egg activation: from Ca2+ spiking to cell cycle progression. http://www.ncbi.nlm.nih.gov/pubmed/16322541
Mammalian eggs arrest at metaphase of the second meiotic division (MetII). Sperm break this arrest by inducing a series of Ca(2+) spikes that last for several hours. During this time cell cycle resumption is induced, sister chromatids undergo anaphase and the second polar body is extruded. This is followed by decondensation of the chromatin and the formation of pronuclei. Ca(2+) spiking is both the necessary and solely sufficient sperm signal to induce full egg activation. How MetII arrest is established, how the Ca(2+) spiking is induced and how the signal is transduced into cell cycle resumption are the topics of this review. Although the roles of most components of the signal transduction pathway remain to be fully investigated, here I present a model in which a sperm-specific phospholipase C (PLCzeta) generates Ca(2+) spikes to activate calmodulin-dependent protein kinase II and so switch on the Anaphase-Promoting Complex/Cyclosome (APC/C). APC/C activation leads to securin and cyclin B1 degradation and in so doing allows sister chromatids to be segregated and to decondense.
Spindle dynamics during meiosis in Drosophila oocytes
J Cell Biol. 1997 Jun 16;137(6):1321-36. Endow SA, Komma DJ.
Department of Microbiology, Duke University Medical Center, Durham, North Carolina 27710, USA. firstname.lastname@example.org Abstract Mature oocytes of Drosophila are arrested in metaphase of meiosis I. Upon activation by ovulation or fertilization, oocytes undergo a series of rapid changes that have not been directly visualized previously. We report here the use of the Nonclaret disjunctional (Ncd) microtubule motor protein fused to the green fluorescent protein (GFP) to monitor changes in the meiotic spindle of live oocytes after activation in vitro. Meiotic spindles of metaphase-arrested oocytes are relatively stable, however, meiotic spindles of in vitro-activated oocytes are highly dynamic: the spindles elongate, rotate around their long axis, and undergo an acute pivoting movement to reorient perpendicular to the oocyte surface. Many oocytes spontaneously complete the meiotic divisions, permitting visualization of progression from meiosis I to II. The movements of the spindle after oocyte activation provide new information about the dynamic changes in the spindle that occur upon re-entry into meiosis and completion of the meiotic divisions. Spindles in live oocytes mutant for a loss-of-function ncd allele fused to gfp were also imaged. The genesis of spindle defects in the live mutant oocytes provides new insights into the mechanism of Ncd function in the spindle during the meiotic divisions.